1221556839 has 4 divisors (see below), whose sum is σ = 1628742456. Its totient is φ = 814371224.

The previous prime is 1221556823. The next prime is 1221556849. The reversal of 1221556839 is 9386551221.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1221556839 - 2⁴ = 1221556823 is a prime.

It is a super-2 number, since 2×1221556839² = 2984402221815343842, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1221556839.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221556849) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 203592804 + ... + 203592809.

It is an arithmetic number, because the mean of its divisors is an integer number (407185614).

Almost surely, 2^1221556839 is an apocalyptic number.

1221556839 is a deficient number, since it is larger than the sum of its proper divisors (407185617).

1221556839 is an equidigital number, since it uses as much as digits as its factorization.

1221556839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 407185616.

The product of its digits is 129600, while the sum is 42.

The square root of 1221556839 is about 34950.7773733289. Note that the first 3 decimals coincide. The cubic root of 1221556839 is about 1068.9840530039.

The spelling of 1221556839 in words is "one billion, two hundred twenty-one million, five hundred fifty-six thousand, eight hundred thirty-nine".